A number of immunoassay systems have been developed utilizing immunologic technology. In these systems, the presence of an antigen in a test sample is detected by causing the antigen to bind to antibodies in a selected testing medium and then detecting the presence of the antigen in the testing medium. In a recently developed system, the testing procedure and the time to carry out the testing process has been substantially reduced so as to make it convenient to carry out the immunoassay process in a doctor's office or by a patient at home.
The prior art system, as shown in FIG. 1, comprises a container 11, housing an absorbent cylinder 13, which serves as a reservoir. On top of the reservoir is a porous plastic disk 15 on which is supported a porous membrane 17, usually separated from the porous plastic disk 15 by a porous contact pad 19. In the immunoassay process, antibodies specific to the antigen being detected are deposited on the membrane 17 by first bonding the antibodies or adsorbing the antibodies on microspheres of a synthetic resin such as polystyrene or latex and then depositing these microspheres in or on the membrane by passing liquid in which the microspheres are suspended through the membrane. A test sample to be tested for the presence of the suspect antigen is poured on the membrane 17 and is drawn through the membrane 17 relatively rapidly by capillary action of the reservoir 13 in combination with the porous plastic disk 15 and the contact pad 19. If the suspect antigen is in the test sample, it will bind to the antibodies deposited on or in the membrane. Following this step, liquid containing labeled antibodies specific to the suspect antigen is poured onto the membrane and is drawn through the membrane into the reservoir 13 by capillary action. If the antigen has been extracted from the test sample and retained in or on the membrane, the labeled antibodies will bind to the antigen and thus remain in or on the membrane 17. The application of the labeled antibody to the membrane will usually be followed by a rinsing step to remove unbound labeled antibody. This rinsing step is then followed by a step of causing the labeled antibody to exhibit its presence. In the case of an enzyme label, this last step is carried out by addition of a solution of a color-forming agent which reacts with the enzyme as the solution passes through it. As each liquid is passed through the membrane it is absorbed by the reservoir and the reservoir must be large enough to hold all of the volume of the test specimen, the labeled antibody solution, the rinse solution and the color-forming solution.
To obtain an accurate indication of the presence or absence of the antigen, the system must cause an even, consistent flow of the various liquids which are passed through the membrane. In order to achieve this even flow, contact between the various components of the system must be maintained. Any gaps between any two of the components will create pools of stagnant liquid and interfere with the capillary action drawing the liquid into the reservoir . This interference leads to erroneous or vague test results. Thus, when assembling the components of the system, great care must be taken to avoid trapping any particulate matter between the components, which particulate matter would create gaps between the components. The material of the membrane is available only as relatively large flat sheet and they must be cut into disks for use in the system. The assembly of the components is difficult because both the membrane and the contact pad are flimsy and manual assembly is usually required.